🚀 go-pugleaf

On Aug 7, 5:04 pm, Jon Kirwan <j...@infinitefactors.org> wrote:
> On Tue, 7 Aug 2012 12:42:56 -0700 (PDT), George Herold
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> <gher...@teachspin.com> wrote:
> >On Aug 7, 3:19 pm, Jon Kirwan <j...@infinitefactors.org> wrote:
> >> On Tue, 7 Aug 2012 05:23:52 -0700 (PDT), dp <d...@tgi-sci.com>
> >> wrote:
>
> >> >On Aug 7, 5:11 am, Jon Kirwan <j...@infinitefactors.org> wrote:
> >> >> ...(Most of my work was in the
> >> >> visible, near UV, and near IR -- but for very different
> >> >> applications.) I still have some decent setups here and I've
> >> >> designed some devices that can be made for only a few
> >> >> dollars, and wavelength calibrated for $8 more, so that high
> >> >> school students could actually built their own real-world
> >> >> equipment that could genuinely "do science" and meet
> >> >> calibration standards. No intensity calibration, though,
> >> >> sadly. That costs money to do. (Unless you have a suggestion
> >> >> about how to do it on the cheap?)
>
> >> >Oh no, I could not possibly have a suggestion. My spectrometers
> >> >don't seem to have an overlapping wavelength range with yours,
> >> >mine are xray/gamma. I am practically clueless when it comes to
> >> >those in the UV and below range, mine generally count single
> >> >photons.
>
> >> For all those reasons, that is why I would LOVE to see the
> >> "optics" (and the schematics, as well.) Totally new area for
> >> me to learn about. In my region, it's all about electron
> >> transitions -- and no molecular dissassociation.
>
> >> I'd expect you'd count single photons at those energies --
> >> just one probably creates quite a shower to deal with. I'd
> >> like to know, in practice, how one measures the energy.
>
> >> Also, in space there is a serious problem with "brown crud",
> >> which is smashed, charged particles that come from the
> >> satellite's own fabrication scattered into space, which
> >> because it is charged comes back to the spacecraft at some
> >> later time, but sticks elsewhere (not where you want it.) I
> >> don't know if there is a problem with this on Mars -- there
> >> is an atmosphere of sorts. But I'm curious just the same if
> >> there is an accumulation problem and how it is dealt with.
>
> >> >Efficiency calibration is costly on those for gamma, too,
> >> >though - the calibration source costs thousands. The rest, hm,
> >> >has become much less expensive since the release of the
> >> >netmca-3 (one can still spend tens of thousands on it but
> >> >does not have to any longer).
>
> >> Now THAT I totally believe. I probably couldn't afford it.
> >> But I still could learn.
>
> >> >I would be curious what gamma spectrometry the thing is
> >> >carrying on board, too (if any, but likely so). Unlikely
> >> >HPGe, but then who knows, Mars is a cold place, they may
> >> >have figured some practical way to cool things down to
> >> >about liquid nitrogen.
>
> >> Well, they certainly don't have much atmospheric pressure to
> >> worry about.
>
> >> Which reminds me of another thing. How do they convect the
> >> internally generated heat away. I recall hearing about
> >> multiple power systems, operating around 32V at near 2A. More
> >> than one. This power must be convected/conducted away -- no
> >> way they want to radiate it. I wonder if they push it
> >> (costing more heat) towards a vane or arm and drag it around
> >> on the surface to get rid of it?
>
> >The atmosphere won't help much.
>
> >Why not?  Thermal conductivity of air is pretty much constant till you
> >get below 1 Torr or so.  Wiki says the mean pressure on mars is about
> >0.1 psi, which is ~5 torr.
>
> Good point.
>
> What triggered my comment is remembering that heat buildup
> was most certainly a problem during broadcasts with the high
> gain antenna system towards Earth. They can't operate it
> continuously, if I recall correctly. Made me wonder about the
> rest. I had also remembered the case of satellites and "knew"
> that the Martian atmosphere could be as little as a few tens
> of Pascals. So I projected that heat accumulation may be a
> problem. Apparently, it isn't.
>
> I gather your point. To understand it more fully, I need to
> think more closely about mean-free-path, I guess. Thanks.

There may be less convection on Mars.  I don't know how that changes
with pressure.
(But there must be some change, Someone makes 'convectron' thermal
couple gauges that give readings up to an atmosphere.  (760 Torr)
>
> >Re spectrometer calibration:  We had this "black body" source. (from
> >Ortec?)  That could be used for intensity calibration.  PITA though.
>
> The problem for students is that they cannot afford the $800
> it takes to get a $8 tungsten bulb calibrated. (It can cost a
> lot more than that, too.) Then they need to set up a careful
> station for making the calibration. It's just plain too
> expensive to do. And I don't know a way around it. Wavelength
> calibration is CHEAP!! $12 buys a merc-argon calibration
> lamp, which fires up with the Argon first (for about a minute
> or two where you get some very nice Argon lines in the longer
> wavelengths) and then the Mercury kicks in and dominates with
> it's lines. A couple of well-timed snapshots and you've got
> enough (with software) to completely calibrate your pixel
> positions in a cheap ($10) megapixel camera.
>
> I'd LOVE to figure out a cheap intensity calibration setup,
> though. So would a lot of other people, I suppose.
>
> >But maybe you could do something on the cheap with a tungsten light
> >bulb.
>
> But that's the problem. I can get a cheap tungsten lamp. They
> are VERY CHEAP. In fact, the EXACT SAME ONE I would buy,
> calibrated, is dirt cheap uncalibrated. It is the calibration
> data that comes with a newly calibrated lamp that costs so
> darned much. It needs to be traceable to standards. And you
> pay for that. Plus, you need an expensive power supply to
> operate it (0.1% current control is standard.) And it ages,
> too. Within 100 hours or so, it's drifted enough that it
> needs recalibration.

OK first a disclaimer, I know squat about the details of spectrometer
calibration.

It would seem to break down into two pieces.  Absolute sensitivity (at
one wavelength) and then relative wavelength sensitivity.

For the first part you could maybe do something with a laser diode
into photodiode and then the same laser (though a bunch of
attenuators) into the spectrometer.

For the second you have the students use the black body curve and the
tungsten lamp.  Operate the lamp at two different temperatures.
(Maybe build a nice stable DC supply for the lamp.)  It seems like you
should be able to extract an approximate sensitvity curve from two
black body curves, even if you don't know the exact temperatures.
(But I'll leave that as an excersise for the students :^)

How good a calibration do you need?

George H.
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> Thanks,
> Jon- Hide quoted text -
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